In our latest Insight, Kechang Niu of Nanjing University talks about the importance of individual variation in harsh environments, the background to his latest paper Harsh environmental regimes increase the functional significance of intraspecific variation in plant communities Nanjing University, and his unusual path into ecology.
About the study: from a plant’s perspective
As a plant standing on this highland, I am defined by a suite of unique traits that not only mirror my ancestral characteristics (i.e. species traits) but also reflect both my ways to adapt and plastically respond to the harsh and unpredictable environment, and my ways to help my conspecific and heterospecific neighbors. How my traits deviate from other individuals of my species is a function of trait differences among those of us belonging to the same ancestor, termed Intraspecific Trait Variation (ITV). Many factors can influence ITV ─ too many to discuss here. I prefer telling you some advantages that ITV can confer on my population and the community of plant species of which I am part of. These include increasing the otherwise low variability among the relatively few species able to occupy such a harsh environment, helping us to resist unpredictable environmental conditions and human disturbance in diverse ways, and supporting us to silently survive in diverse micro-habitats despite an overall shortage of resources.
People traditionally were happy just to call me and my conspecifics by our species name, caring little about individuality ─ our ITV. Much to my surprise, they randomly measured some traits on a few of us to characterize the fitness of our entire population and the functional dynamic of our community. Recently, they seem to care a lot about the functional significance of our differences for the health and vitality of our community. Maybe they have noticed the increasing number of species lost from our community under their disturbances, and are worrying about the ecosystem services that we provide to them. This reminds me that Dr. Niu says there is not much ITV in benign, resource-rich sites. If that is true, we are more proud of our diversity, but who knows how he gets such strange ideas. Whatever, we’ll just be ourselves, quietly watching what will happen in this rapidly changing land.
About the research: known unknowns
Fifteen years ago, when I began my study of plant community dynamics in alpine meadows on the Tibetan Plateau and in the French Alps, I decided it was important to measure functional traits on individual plants simply because it was clear that traits were very different among the individuals in a population, not just among populations distributed in different places. When I calculated functional diversity, I had to write my own code since existing approaches like the ‘FD’ package in R considered only species level traits. At that time, I was also heartened by my colleagues in France; they highlighted not only the importance of species traits in community functional dynamics, but also of ITV. The last five years I have been puzzled that some ecological literature raised doubts about the existence of distinct patterns of ITV in plant communities. Meanwhile, other ecologists noticed that including ITV challenges the expected pattern of diversity in communities, suggesting a nonrandom community ITV. I took a closer look at this topic and found that there were competing hypotheses about the association between species diversity and ITV in communities. Some hypotheses predicted ITV in the community should decrease with increasing species diversity due to niche-packing, e.g. diverse species restrain expression of heritable traits, but others predicted an increase with species diversity due to individual differences facilitating coexistence of species. Moreover, a specific pattern of ITV at the population level was well-documented in evolutionary biology: stress-induced phenotypic variation was evident in populations of various species, which should scale up to the community level. Additionally, our studies in Tibetan meadows had shown some differences in ITV across communities distributed along environmental gradients. In short, both theoretical research and my intuition based on field work convinced me there should be differentiated patterns of ITV in ecological communities that varied in environmental harshness. The question became why we did not find such a pattern in our data.
The nature of human understanding of any topic can be problematic — too confident of the part that we know, and too inattentive to the part we do not know. This inattention too often leads to inappropriate interpretation of existing data. For example, we focus on within-population ITV, when between-population ITV may better reflect the effect of abiotic factors on ITV in different communities. We extract ITV from changes in Community- Weighted-Mean trait values, unconcerned that these are determined largely by dominant species that turnover across communities over space. Based on lessons from relevant studies, in this study, we created a conceptual framework to hypothesize how the ITV within communities and its importance relative to interspecific trait variation (rITV) will increase with environmental harshness. We propose a novel analytic method to calculate ITV and rITV. Then, by assuming positive association between within- and among-population ITV, we experimentally tested this hypothesis in Tibetan alpine meadow communities distributed in contrasting environmental regimes. Results clearly show that rITV increases with environmental harshness not only because of decreasing interspecific variation but also increasing ITV, an opposing response of intraspecific and interspecific variation to availability of soil phosphorus. These results not only support our prediction, but also suggest that ITV can act as a buffering mechanism for species turnover or loss.
Such a buffering role of ITV in stabilizing community functional structure is expected by eco-evolutionary dynamic theory, but rarely reported in field studies. Therefore, from my point of view, this study illustrates that integrating ITV in community ecology studies will facilitate our understanding about how the interplay between evolutionary and ecological processes shape future diversity patterns from local to landscape and even broader scales, potentially challenging some preconceptions and answering some unresolved questions. For example, to what extent might the effect of the rapid evolutionary processes indicated by ITV offset the effects of species loss on community function? Or, in response to changing environment, might ITV induce loss in community function even though species composition and diversity did not change much? It is also possible that with a deeper understanding of nature, not only our experimental results but also our analytic method and hypotheses will be proven partly or entirely wrong. No matter, what could be better than the challenge of advancing and answering exciting questions in community ecology in the light of evolutionary biology. I am always ready for that adventure.
About the author: a lost Lama
My early interests were in history, math, and philosophy – far away from questions in evolutionary biology or the economy of nature. It was an odd and, in some ways, sad set of circumstances that led me to become an applied ecologist. As the second son of a typical Tibetan family in a small village near the Labrang Monastery, I was born to be a Lama. I ended up going to school instead of to the monastery only because my master (a Lama uncle of my grandpa) died when I was 5 years old. As my studies advanced, I was selected to go to the Northwest Normal University for training as a middle school teacher. There, I had little choice but to study biology because in 1998 the only majors open to minority students were Biology and Chinese. I was lucky that later I had the opportunity to pursue a Ph.D. in ecology, which I hoped would let me do something useful to protect the rangelands where I grew up. The Tibetan rangelands have undergone increasing degradation over the last four decades, with no one clearly understanding why. In the last few years, we have written papers revealing that ITV mediates the functional response of the rangeland plant community to soil phosphorus deficiency, resulting in a biodiversity imbalance that ultimately leads to the degradation of rangeland function and a reduction in ecosystem services. Under the changes in land use and climate conditions I have observed over just my own lifetime, it sometimes seems that none of us can do enough to prevent the loss of my homeland and the diversity on Earth.
That said, I am happy to have the opportunity to write this essay to remind people worldwide that every individual plant or person is characterized by unique traits that matter not only for themselves and their community, but also for humankind! For myself, I do not entirely know what the future holds. So long as I am able survive in such academic environment, I am confident I will continue to learn more about the plants, animals, microorganism, pastoralism and the ecological network on the Tibetan Plateau ─ especially, why the biota has been able to quietly thrive for thousands of years. I will keep telling my students and our kids how beautiful and smart these silent lives are!